Fall Garden Cleanup Q and A

Here are some questions we've received about fall cleanup in the garden, along with the answers given by our regional horticulture staff.

Cutting Back Perennials

Question: After the first frost, is it okay to clean out my perennial garden by cutting back the flower stalks? Or is it best to just leave them as is and cut them back in the spring. I'm thinking of my phlox, coreopsis, and daylillies, for example.

Answer: Here are some pointers on overwintering from Perennials for Dummies by Marcia Tatroe and NGA. 1. Cut back on watering as temperatures cool. This signals plants that it's time to go into dormancy and helps harden them off. 2. If plants were bothered by pests or disease problems, remove all plant debris and apply mulch under plants to reduce numbers of overwintering eggs and disease spores. 3. Place a fresh 4- to 6-inch layer of organic mulch around the base of the plants. 4. If your temps. are regularly below 0° F, don't cut back the perennials until late winter or early spring. The dead foliage helps protect them from cold. 5. After the ground freezes, cover the whole bed with a loose layer of straw or hay. Leave it until early spring and then gradually remove it as temperatures warm. Don't remove it all at once.

Making Leaf Mold

Question: I read somewhere that you can create your own leaf mold to add to the soil. The process involved putting leaves in a garbage bag and poking holes in it for air. Then you let it sit a few months and the leaves will decompose. Would you have to add water or soil or anything else to help it? Can I do this with all the leaves I rake up? I have a storage shed I could put them in over the winter.

Answer: Leaf mold is simply partially decomposed leaves. Leaves in a pile outdoors will eventually become leaf mold all on their own, just as they would on the ground in the forest. In my experience, simply putting the leaves in a bag for a few months does not work at all. They need to be dampened and, since leaves are very high in carbon, you will also need to add a source of nitrogen (such as fertilizer or fresh barnyard manure) in order for them to begin to compost. They should be stored well above freezing, because the colder the temperature the slower the process; warm temperatures are really best. Chopping the leaves will also speed things up, as will stirring the mixture from time to time. Instead of composting the leaves, you could simply chop them and use them as mulch. They will break down over time and feed the soil that way, too.

Crop Rotation

Question: As I clean up my garden I am beginning to prepare some beds for next spring. I know I should rotate my crops. How many years do I need to wait before I plant my tomatoes in the same bed? How far away do the new beds need to be from the original?

Answer: Three to five years is the normal range for rotation of tomatoes; five years is being better but rather difficult in a small garden. Here is an example of a rotation. Divide the garden into three areas, A, B, and C. Plant tomatoes in part A the first year, part B the second year and part C the third year, and start the cycle over in year four. Tomatoes, potatoes, eggplants and peppers should be considered together as a group for rotation purposes because they suffer from many of the same pest and disease problems. Since there are other vegetables that also should be rotated, such as the cucmber/squash/pumpkin/melon group, this works out rather well. The distance between the areas is not that important because the rotation is aimed at avoiding a buildup of soil-borne problems and allowing time to rebuild the soil thoroughly between crops. A good fall cleanup routine helps reduce insect and disease problems that linger on plant residues.

Fall Cleanup

Question: What should I do to clean my beds of all plants and leaves so that insects will not overwinter in my vegetable garden? And should I leave a covering of plants and leaves to act as a mulch and provide food for the beneficial worms?

Answer: In my garden I like to remove the fallen leaves and plant debris and add them to the compost heap. I discard any diseased material, such as rose leaves with black spot; this type of material should not be added to a compost heap or left in the garden because it can harbor and spread the disease. Rather than adding the spent plants to a compost pile, another option is to gather up all of the leaves and assorted plant debris and run over it with a mulching mower, then place the material back on the beds to act as a nutrient-rich mulch. This will also encourage earthworms and control weeds.

Pruning Ornamental Grasses

Question: What is the proper method of cutting back ornamental grasses for the winter in northern climates?

Answer: Most gardeners wait at least until after the grasses have bloomed so that they can enjoy the ornamental plumes each fall season. (The seedheads are also attractive in winter, so I like to wait until spring to trim them.) Then, cut the dead grasses back to about 6 inches; the new growth will quickly cover the old stubs. Some gardeners use a hedge trimmer, as this is much faster than using a hand clipper.

Plowing vs. Scraping the Garden

Question: Would it better to plow plant residues into the garden or to scrape the garden clean with my tractor's front end loader at the end of the season? I have done my gardening in a community garden for several years now, and would like to offer my services to the park district that cares for it. The soil is heavy clay and many of the gardens are quite weedy.

Answer: I don't recommend scraping clean with heavy equipment because it will compact the soil, which is not a good thing, especially with heavy clay. Plant roots need an aerated soil to be able to move easily through it. Tilling in leftover vegetable and flower plants would be okay,as long as there aren't disease problems. But definitely don't plow under the weeds at the end of the season, as they will have likely already gone to seed. You'll just be planting the seeds! The best thing would be to remove and fully compost the plant material, then add that to the soil. A winter cover crop would protect the soil and add organic matter, too.

Winter Protection for Perennials

Question: I am confused about how to protect my perennials in the winter. Should I put a mulch on them? After or before the ground freezes? Should I water them through the fall, or let them dry out?

Answer: Perennials have developed the ability to survive winter, often in the wild and unattended. Assuming the plants are rated hardy in your zone, and that drainage in your garden is good, you shouldn't have to worry. Woody plants and evergreens in particular survive winter better when they are fully hydrated when the cold weather comes. For perennials, make sure the soil is moderately moist going into winter -- just like when they're growing too much or too little moisture is a problem for dormant plants. In many regions fall rains are sufficient to keep the soil moist; it stays moist longer during cooler weather than it does during the summer. It's a good idea to maintain a 2- to 3-inch layer of mulch during the summer and to leave it there through the winter. In cold weather the mulch helps keep the soil from freezing and thawing when temperatures fluctuate and thus limits "heaving," which is when plants are popped out of the ground. Marginally hardy plants benefit from the addition of a protective mulch. Straw is a good choice because it is light and insulates well. Many books will tell you to mulch "after the ground is frozen" but in some areas it may never freeze solid. In this case, simply wait until there has been a good killing frost or two and the rodents have all found homes elsewhere, and then apply your protective mulch.

Composting Leaves

Question: I have never composted before. I would like to make a 4x4x4 fenced-in area and compost fall leaves. If I fill the bin in early November will the leaves decay by the middle of May, when I can rototill them into the soil?

Answer: Composting essentially stops when the weather turns cold, and plain fallen leaves alone can take a year or more to decompose. To speed up the process you can shred the leaves and till them in this fall. By spring when planting time comes they should be decayed enough for planting.

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